[46.06] Interstellar Medium from Refractive Scintillation of Pulsars

We developed the theory of refractive scintillations for pulsar
emission for two types of spectra of electronic density fluctuations
in the interstellar medium: a power spectrum, and a piece-power spectrum.
We have obtained expressions for the parameters of the refractive
scintillations for the cases of a uniform distribution of electron
density irregularities along the line of sight, for a phase screen,
for the medium irregularities being located close to the pulsar, and to
the observer. Based on the data from 5 years of observations of the
variation of the flux of 21 pulsars at the frequency of 610MHz we
show that the interstellar medium for DM > 30 pc/cm^3 is very
inhomogenous, and variations of the scintillation parameters are
mainly due to variations of the electron density, and are not
due to the distance to the source. We show how we can estimate the
location of the effective layer of the turbulent medium responsible
for the scintillations, as well as the thickness of the layer.
These parameters were computed for the observed pulsars.
We show also that in the interstellar medium there are two type
of spectra: a power spectrum, and a piece-power spectrum. The
characteristic scale at which the break happens in the spectrum is
l\sim=3*10^10cm. We also show that a pure power spectrum happens
in a diffuse medium which is filled approximately uniformly
along the line of sight, and the spectrum with a break happens in the
medium where there are compact regions with an increased electron
density.